U.S. Department of the Interior 

U.S. Geological Survey

Surveys of Water Velocities in the 

Vicinity of the Discharge-Release Gates 

of Salamonie Lake Dam, 

Northeastern Indiana, Spring and Winter 1998

By Scott E. Morlock and James A. Stewart

Open-File Report 99-228

Prepared in cooperation with the 

U.S. Army Corps of Engineers

Indianapolis, Indiana 

2000
U.S. Department of the Interior 

BRUCE BABBITT, SECRETARY

U.S. Geological Survey 

Charles G. Groat, Director

The use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

For additional information, write to:

District Chief

U.S. Geological Survey

5957 Lakeside Boulevard

Indianapolis, IN 46278-1996

Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Federal Center

Denver, CO 80225-0286
Contents

Abstract ................................................................................... 1

Introduction ................................................................................ 1

Purpose and Scope ...................................................................... 2

Physical Setting......................................................................... 2

Methods of Investigation ...................................................................... 2

Acoustic Doppler Current Profiler .......................................................... 5

Global Positioning System ................................................................ 5

Water-Velocity Surveys....................................................................... 6

Data Collection......................................................................... 6

Data Processing......................................................................... 6

Spring Water-Velocity Survey ............................................................. 7

Winter Water-Velocity Survey............................................................. 7

Summary and Conclusions. .................................................................... 11

References ................................................................................. 11

Figures

1. Map showing location of study area ...................................................... 3

2. Photograph of Salamonie Lake dam spillway tower.......................................... 2

3. Photographs of boat-mounted acoustic Doppler current profiler and global positioning system mobile

receiver ............................................................................ 4

4. Diagram showing locations of acoustic Doppler current profiler transects collected during a spring

and a winter water-velocity survey at Salamonie Lake, northeastern Indiana ...................... 8

5. Water-velocity-contour plot along a transect in the vicinity of the Salamonie Lake spillway tower, 

northeastern Indiana, on April 24, 1998, during a period of discharge release of 4,700 cubic feet 

per second .......................................................................... 9

6. Water-velocity-contour-plot along a transect in the vicinity of the Salamonie Lake spillway tower, 

northeastern Indiana, on December 4, 1998, during a period of discharge release of 3,200 cubic 

feet per second....................................................................... 10

Contents iii
Conversion Factors, Unit Abbreviations, and Vertical Datum

Multiply

foot (ft)

foot per second (ft/s)

 3

cubic foot per second (ft /s)

square mile (mi )

acre

acre-foot (acre-ft)

By

0.3048

0.3048

0.02832

2.590

0.4047

1233

To obtain

meter

meter per second

cubic meter per second

square kilometer

hectare

cubic meter

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) 

a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, 

formerly called Sea Level Datum of 1929.

iv Surveys of Water Velocities in the Vicinity of Discharge-Release Gates, Salamonie Lake, Northeastern Indiana
Surveys of Water Velocities in the Vicinity of the 

Discharge-Release Gates of Salamonie Lake Dam, 

Northeastern Indiana, Spring and Winter 1998

By Scott E. Morlock and James A. Stewart

Abstract

Two water-velocity surveys in the vicinity 

of the discharge-release gates were performed 

at the Salamonie Lake flood-control reservoir 

in northeastern Indiana during periods of highdischarge release. One survey was done in 

the spring when the reservoir pool was at a 

high elevation; the other survey was in the 

winter when the reservoir pool was low.

The maximum measured velocity 

was 2.4 feet per second for the spring survey and 1.9 feet per second for the winter 

survey. The maximum measured velocities 

occurred in the immediate vicinity of the spillway tower containing the discharge-release 

gates. Velocity-field magnitudes diminished 

rapidly with distance from the tower. Beyond 

an estimated 40 feet from the tower, velocity 

magnitudes were below 0.5 feet per second.

For the spring and winter surveys, data 

were collected along four transects that were 

parallel to the face of the spillway tower. The 

transects were at the following approximate 

distances from the spillway tower: 900, 600, 

and 300 feet and as close to the tower as 

practical. For the spring and winter surveys, 

velocity-contour plots were produced for 

the transects closest to the tower. Plots were 

not made for the transects at 900-, 600-, and 

300-foot intervals because velocities were 

negligible at these distances.

An acoustic Doppler current profiler 

(ADCP) mounted on a boat was used to collect 

velocity and depth data and to compute positions of the velocity and depth data relative 

to the boat track. A global positioning system 

(GPS) mobile receiver was used to collect 

earth-referenced position data, and a GPS 

base-station receiver was used to improve the 

accuracy of the earth-referenced position data. 

The earth-referenced position data were used 

to transform the ADCP-computed positions 

(which were relative to the boat tracks) to 

positions referenced to a point on the spillway tower.

Introduction

Salamonie Lake is a flood-control reservoir 

in northeastern Indiana. The dam is an earthen 

structure, and the main spillway is a concrete tower 

with three submerged discharge-release gates. 

The reservoir dam and spillway are operated 

by the U.S. Army Corps of Engineers (USAGE). 

The Indiana Department of Natural Resources, 

Division of Fish and Wildlife, expressed concern 

to the USAGE that during high-discharge releases 

from the spillway gates, large numbers of fish 

might be drawn through the spillway, forcing 

them to migrate downstream from the lake. 

The USAGE then requested the assistance of the 

U.S. Geological Survey (USGS) to perform two 

water-velocity surveys during periods of high 

release in the vicinity of the discharge-release 

gates, one in spring at a relatively high pool elevation and one in winter at a lower pool elevation.

Abstract 1
To perform the surveys, the USGS used 

acoustic Doppler current profiler (ADCP) and 

global positioning system (GPS) technologies 

to collect water-velocity and position data. The 

ability of an ADCP to rapidly obtain verticalvelocity profiles from a moving boat and the 

ability of GPS receivers to accurately compute 

earth-referenced positions allowed the surveys 

to be completed much faster and with greater 

accuracy than if conventional methods (such as 

mechanical current-meter measurements) had 

been employed.

Purpose and Scope

This report describes the use of ADCP and 

GPS technology for water-velocity surveys and 

presents the results of two water-velocity surveys 

in the vicinity of the Salamonie Lake dischargerelease gates.

Physical Setting

Salamonie Lake, a reservoir in northeastern 

Indiana (fig.l) formed by impoundment of the 

Salamonie River, was completed in 1966 for 

flood control and recreation. Salamonie Lake 

has a capacity of 13,100 acre-ft at the normal pool 

elevation of 730 ft, mean sea level (msl); a surface area of 980 acres (William Byron, U.S. Army 

Corps of Engineers, written commun., May 13, 

1999); and a drainage area of 553 mi2 (Ruddy and 

Hitt, 1990). Seasonal pool elevations range from 

730 to 755 ft, msl (U.S. Army Corps of Engineers, 

1998).

The Salamonie Lake dam is an earthen structure, and the main spillway is a concrete tower 

(fig. 2) with three submerged discharge-release 

gates. Each gate is 4.75 ft wide and 16 ft high, with 

an invert elevation of 684 ft, msl (William Byron,

Figure 2. Salamonie Lake dam spillway tower.

U.S. Army Corps of Engineers, oral commun., 

September 30, 1998).

Methods of Investigation

A boat-mounted ADCP (fig. 3A) was used to 

collect velocity and depth data and compute positions of the velocity and depth data relative to the 

boat track. A GPS mobile receiver (fig. 3B) was 

used to collect earth-referenced position data, and 

a GPS base-station receiver was used to improve 

the accuracy of the earth-referenced position data. 

The earth-referenced position data were used to 

transform the ADCP-computed positions (which 

were relative to the boat tracks) to positions referenced to a point on the spillway tower.

2 Surveys of Water Velocities in the Vicinity of Discharge-Release Gates, Salamonie Lake, Northeastern Indiana
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Methods of Investigation 3
Figure 3. Boat-mounted acoustic Doppler curent profiler (A) and global positioning system mobile receiver (B).

4 Surveys of Water Velocities in the Vicinity of Discharge-Release Gates, Salamonie Lake, Northeastern Indiana
Acoustic Doppler Current Profiler

An ADCP transmits acoustic pulses into the 

water column, receives reflected pulses from suspended particles, and then computes the frequency 

shift between the transmitted and reflected pulses. 

The frequency shift is used to compute particle 

velocities; because the particles are suspended in 

the water column and move at the same velocity 

as the water, water velocities can be computed. By 

timing the receipt of reflected pulses, the ADCP 

computes velocities in successive, uniformly 

spaced volumes called "depth cells" down through 

the water column. Thus the ADCP obtains verticalvelocity profiles, with the velocities reported in 

terms of magnitude and direction at uniformly 

spaced depths. The time it takes to collect a full 

vertical-velocity profile from the ADCP to the bottom of the water column is called an "ensemble." 

Because of limitations in ADCP technology, the 

instruments cannot measure velocities close to 

the surface or bottom of the water column (a detailed explanation of these limitations is given 

in Morlock, 1996).

The ADCP uses the frequency shift between 

transmitted and reflected pulses from a river or 

lake bottom in conjunction with an electronic compass and tilt and roll sensors to compute the speed, 

distance, and direction the boat travels over the 

bottom; this process is called "bottom tracking." 

Total depth of water also is computed. The bottomtracking feature allows the ADCP to compute the 

relative horizontal position of each ensemble in 

terms of an x-y coordinate system (the x-y coordinate system is the distance north and east from the 

starting point of data collection). A boat-mounted 

ADCP therefore is able to collect many ensembles 

in a short time, with each ensemble containing a 

complete vertical-velocity profile with a known 

depth and x-y coordinate. A complete set of ensembles collected along a particular boat track is 

called a "transect."

A portable computer is required to operate 

the ADCP software. The ADCP software allows 

an operator to configure the ADCP and collect, 

view, and store all data in real time (for a more 

detailed description of ADCP theory and operation, see Gordon, 1996).

Global Positioning System

GPS relies on a constellation of 25 earth-orbit 

satellites. A GPS receiver calculates its position 

on earth through "satellite trilateration," the process of computing the intersection of three or more 

spheres, the centers of which are GPS satellites. 

In the interests of national security, the Department 

of Defense can degrade the quality of GPS signals 

with Selective Availability (SA). The absolute 

accuracy of GPS positions is between 25 and 

100 meters because of SA and atmospheric errors 

(for more detailed information, see Baker and 

Morlock, 1996).

The absolute accuracy of data collected with 

a GPS mobile receiver can be improved by differentially correcting the data with a GPS base-station 

receiver. The mobile and base-station receivers 

operate simultaneously. Within 500 kilometers, 

the mobile receiver and base station are influenced 

equally by SA and atmospheric errors (Wilson, 

Morlock, and Baker, 1997). If the location of the 

base-station receiver is known, the positions 

collected by the mobile receiver can be corrected 

by applying the difference between the known and 

computed location of the base-station receiver to 

the data collected by the mobile receiver. If realtime communication between the mobile and 

base-station receivers is possible, the data can be 

differentially corrected as data are collected by the 

mobile receiver. If real-time communication is not 

used, the differential corrections are applied in 

post-processing.

Acoustic Doppler Current Profiler 5
Water-Velocity Surveys

Two water-velocity surveys were made, 

both during periods of maximum release from 

the main spillway. The first survey took place on 

April 24, 1998, at a pool elevation of 761.5 ft, msl 

(normal pool elevation is 730 ft, msl), and the 

second took place on December 4, 1998, at a pool 

elevation of 740.2 ft, msl.

Data Collection

The data were collected in the same manner 

for each of the two water-velocity surveys. The 

USAGE had specified that velocity data were 

required along four transects at the following 

approximate distances from the spillway tower: 

900, 600, and 300 ft and as close to the tower 

as practical. The transects were run parallel to 

the face of the spillway tower containing the three 

submerged discharge-release gates.

A laser range finder was used to place marker 

buoys at specified distances from the spillway 

tower. A 600-kilohertz-frequency ADCP deployed 

from a 16-ft aluminum boat (fig. 3A) was used for 

the surveys. Each ADCP transect was started at a 

marker buoy, and the boat was steered so that the 

boat track was parallel to the face of the spillway 

tower. Transects were terminated when velocities 

appeared to be negligible or when the water depth 

became too shallow for the ADCP to operate.

The transects had lengths that ranged from 

450 to 650 ft for the spring survey and from 250 

to 450 ft for the winter survey. During the winter 

survey, the pool elevation was lower than for the 

spring survey; subsequently, the reservoir in 

the vicinity of the spillway tower was not as wide 

and the transects were shorter. The depth-cell 

length was set so the ADCP reported a velocity 

about every 3 ft in the vertical, starting at a depth 

of about 8 ft. The ADCP used for the surveys could

not measure velocities within about 8 ft from the 

surface and 4 ft from the lake bottom. The accuracy of the velocity measurements was estimated 

tobeO.lOft/s.

A GPS mobile receiver (fig. 3B) was used 

to collect earth-position data for each of the corners of the spillway tower and at the marker buoys 

that identified the start of each ADCP transect. 

The GPS mobile receiver did not have real-time 

telemetry with the GPS base-station receiver; the 

position data were differentially corrected in postprocessing.

Data Processing

The ADCP processing software was used to 

output the following data for each ensemble to text 

files: ensemble number, ensemble position, depth 

of velocity measurement, and velocity magnitude 

and direction. The GPS-collected data were differentially corrected with a first-order base-station 

receiver at the USGS Indianapolis office. A "firstorder station" means that the position of the station 

is known with an accuracy of 10 centimeters over 

10 kilometers (Baker and Morlock, 1996).

Because ADCP positions are referenced relative to the start of an individual transect, a common 

coordinate system was needed for all survey data. 

The surveys were undertaken to provide data on 

the effect of high-discharge release through the 

spillway-tower gates upon the velocity field: all 

data, therefore, were referenced to a point on the 

spillway tower. The southwest corner of the spillway tower was selected as the reference. The GPS 

position provided latitude-longitude points for 

the southwest corner of the spillway tower and 

the start points of each transect. Knowing that 

1 second of latitude equals 101 ft and 1 second 

of longitude equals 77.6 ft at the study location 

(Wilson, Morlock, and Baker, 1997), the distance 

of each transect start point in feet north-south 

and east-west from the southwest spillway-tower

6 Surveys of Water Velocities in the Vicinity of Discharge-Release Gates, Salamonie Lake, Northeastern Indiana
corner was computed. ADCP ensemble positions, 

which were referenced to the transect start points, 

then were transformed with computer spreadsheet programs so that all data collected with the 

ADCP were referenced to the southwest corner of 

the spillway tower. The text files that contained the 

ADCP data with positions referenced to the spillway tower then were ready for analysis and for 

use in generating velocity-contour plots. A computer software package, ARC/INFO (a geographic 

information system), was used to generate graphics 

plots of the velocity-survey data.

Spring Water-Velocity Survey

The spring survey took place on April 24, 

1998, at a pool elevation of 761.5 ft, msl (Jamie 

Evans, U.S. Army Corps of Engineers, oral commun., May 7, 1999). The discharge released from o

the spillway during the survey was 4,700 ft/s 

(William Byron, written commun., May 13, 1999). 

The four transects used for the survey were 

assigned numbers IS through 4S. Transect IS 

was about 20 ft from the tower face; transects 2S 

through 4S were about 300, 600, and 900 ft, 

respectively, from the tower face (fig. 4).

The greatest velocity measured was along 

transect IS (the velocities in this and subsequent 

discussions are horizontal velocities; verticalvelocity magnitudes were generally less than 

0.5 ft/s for all collected velocity data). The magnitude of this velocity was 2.4 ft/s, and the 

direction was 350 degrees (referenced to true 

north). The velocity occurred at a depth of 67 ft 

(694.5 ft, msl), about 3 ft south and 15 ft east of 

the spillway-tower southwest corner. Velocities 

were greatest within about 40 ft of the spillway 

tower; beyond this distance, velocities at all 

measurement depths decreased below 0.5 ft/s.

The magnitudes, depths, and directions of the 

velocities within 40 ft of the spillway tower were 

consistent with a flow pattern into the submerged 

discharge-release gates. The figure 5 plot shows 

velocity contours along transect IS. Velocities 

measured along transects 2S, 3S, and 4S were less 

than 0.5 ft/s and did not have consistent directions.

Winter Water-Velocity Survey

The winter survey took place on December 4, 

1998, at a pool elevation of 740.2 ft, msl (Jamie 

Evans, oral commun., May 7, 1999). The discharge 

released from the spillway during the survey was

o

3,200 ft/s (William Byron, written commun., 

May 13, 1999). The four transects used for the 

survey were assigned numbers 1W through 4W. 

Transect 1W was about 30 ft from the tower face; 

transects 2W through 4W were similar distances 

from the tower as the corresponding spring-survey 

transects (fig. 4).

The greatest velocity measured was along 

transect 1 W. The magnitude of this velocity was 

1.9 ft/s and the direction was 300 degrees, true 

north. This velocity occurred at a depth of 34 ft 

(706 ft, msl), about 3 ft south and 35 ft east of 

the spillway-tower southwest corner. Velocities 

were greatest within about 40 ft of the spillway 

tower. As in the spring survey, the magnitudes, 

depths, and directions of the velocities within 40 ft 

of the spillway tower were consistent with a flow 

pattern into the submerged discharge-release gates. 

Beyond this distance, velocities at all measurement 

depths dropped below 0.5 ft/s. The figure 6 plot 

shows velocity contours along transect 1 W. Velocities measured along transects 2W, 3W, and 4W 

were less than 0.5 ft/s and did not have consistent 

directions.

Spring Water-Velocity Survey 7
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100

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2W

1S

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EXPLANATION

SPRING SURVEY TRANSECT

WINTER SURVEY TRANSECT

1S TRANSECT LABEL

Note Distances are expressed in feet north and east of the southwest corner of the spillway tower

-400 -200 200 400 600 800

DISTANCE EAST, IN FEET

1,000 1,200 1,400 1,600 1,800

Figure 4. Diagram showing locations of acoustic Doppler current profiler transects collected during a spring and a winter water-velocity survey at Salamonie Lake, northeastern Indiana.
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760 - 750

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EXPLANATION 

.... TOP OF SPILLWAY

_ , o _ WATER VELOCITY, IN 

FEET PER SECOND

ACOUSTIC DOPPLER 

+ CURRENT PROFILER 

DATA POINT

50

- 10

-20

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50 LJJ

-60

-70

- 80

100 150 200 250 300 350 400 450 500 550 600 650 700 750

DISTANCE, IN FEET

Figure 5. Water-velocity-contour plot along a transect in the vicinity of the Salamonie Lake spillway tower, northeastern Indiana, 

on April 24,1998, during a period of discharge release of 4,700 cubic feet per second.
q

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740

SPILLWAY TOWER

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LU 

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EXPLANATION 

..., TOP OF SPILLWAY

T 0 WATER VELOCITY, IN 

FEET PER SECOND

ACOUSTIC DOPPLER 

+ CURRENT PROFILER 

DATA POINT

NE

- 0

- 10- 20

- 30

- 40

- 50

\- LLJ LLJ 

LL

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50 100 150 200 250 300

DISTANCE, IN FEET

Figure 6. Water-velocity-contour plot along a transect in the vicinity of the Salamonie Lake spillway tower, northeastern Indiana, 

on December 4,1998, during a period of discharge release of 3,200 cubic feet per second.
Summary and Conclusions References

Water velocities in the vicinity of the Salamonie Lake discharge-release gates were surveyed 

on April 24, 1998, and December 4, 1998; each 

survey was made during periods of maximum 

release. ADCP and GPS technologies were used 

to complete the surveys. For each survey, velocity 

data were collected along transects made as close 

as possible to the spillway tower containing the 

discharge-release gates and at approximate distances of 900, 600, and 300 ft from the tower. 

The survey data were collected and prepared 

for generation of velocity-contour plots with the 

computer software package ARC/INFO.

The maximum velocities measured during the 

spring and winter surveys were 2.4 and 1.9 ft/s, 

respectively. For both surveys, the velocity-field 

magnitudes diminished rapidly with distance from 

the spillway tower. At distances greater than about 

40 ft from the tower, velocity magnitudes were less 

than 0.5 ft/s.

The velocity surveys could be improved 

by modifying the field-data-collection scheme. 

Instead of running just four transects, a grid of 

transects parallel and orthogonal to the spillway 

tower could be used. The interval between 

transects could be reduced to 50 or 100 ft, which 

would allow horizontal-velocity-contour maps 

for different depths to be produced.

Baker, N.T.. and Morlock. S.E., 1996, Use of a global 

positioning system and an acoustic Doppler current 

profiler to map river and lake bathymetry, in 

Hallam, C.A., Salisbury, J.M., Lanfear, K.J., and 

Battaglin, W.A., eds., Proceedings of the AWRA 

Annual Symposium, GIS and Water Resources: 

American Water Resources Association, Herndon, 

Va., TPS-96-3, p. 373-381.

Gordon, R.L., 1996, Acoustic Doppler current profiler, 

principles of operation A practical primer, second edition for Broadband ADCP's: San Diego, 

Calif., RD Instruments, 54 p.

Morlock, S.E., 1996, Evaluation of acoustic Doppler 

current profiler measurements of river discharge: 

U.S. Geological Survey Water-Resources Investigations Report 95-4128, 37 p.

Ruddy, B.C., and Hitt, K.J., 1990, Summary of selected 

characteristics of large reservoirs in the United 

States and Puerto Rico, 1988: U.S. Geological 

Survey Open-File Report 90-163. 295 p.

U.S. Army Corps of Engineers, Louisville District Daily 

Lake Report, 30 September 1998: From URL 

http://www.orl-wc.usace.army.rnil/reports/ 

lkreport.html, accessed September 30, 1998.

Wilson, J.T., Morlock, S.E., and Baker, N.T., 1997, 

Bathymetric surveys of Morse and Geist Reservoirs in central Indiana made with acoustic 

Doppler current profiler and global positioning 

system technology, 1996: U.S. Geological Survey 

Water-Resources Investigations Report 97-4099, 

49 p.

Summary and Conclusions 11